The winding of a web of material presents a number of difficult problems. In particular, the tension in the web must be closely controlled at all times throughout the winding cycle comprising start of wind, winding and end of wind, so that the web is not ruptured, or stretched beyond its elastic limit, or allowed to become slack, yet at the same time the winding cycle must be as short as possible for efficient economical production. If at any time during winding the web is tensioned to an excessive degree although short of actual web rupture, web distortion occurs and for instance the web becomes necked or rippled, spoiling the appearance of the wound product. If the excessive tension is such as to stretch the web beyond its elastic limit then, in the case where the intended function of the web is to act as a stretchable material to be stretched on application and then allowed to contract to provide an effective seal, the wound web has no utility.
The core on which the web is wound must be of inexpensive construction such as a hollow tube of paper or other relatively inexpensive material which inherently limits the resistance of the core to collapse under pressure. This factor creates special problems since the web material cannot be wound without tensioning same causing at least some measure of stretch and since it is essential to restrict such stretching below the elastic limit of the material the web contracts on the core as soon as it is relieved of the winding tension thereby exerting a progressively increasing pressure on the core as the winding continues tending to cause core collapse. This web memory recovery or contraction occurs while the core is conventionally subject to lateral deflection between its end supports during winding due to web pull on the core, and leads to a high incidence of core collapse or buckling during winding, destroying the product and creating problems for its release from the winding station.
The web itself of course must be wound on the core free from start to finish of folds, creases, wrinkles or other disconformities, and the length of web wound must be held constant to the intended specified length. Apart from the matter of controlling tension in the web during the actual winding operation the severing of the tensioned web when a sufficient length of material has been wound on the core presents special problems. As will be appreciated, as the tensioned web parts it will have a backlash tendency in both directions away from the line of severance and if the trailing edge of the web material wound on the core is not controlled or the web is not uniformly tensioned, such trailing edge will either not lie symmetrically along the outside of the core or will be distorted or ragged and will not lie smooth against the outside of the core. On the other hand, if the flying leading edge of the parent web stock is not properly controlled, start of the winding of the next succeeding core either cannot be effected or, alternatively is effected, but with such leading edge either not lying uniformly along or smooth against the core. Both improper winding starts or finishes affect the acceptability of the product particularly where the web is a clear transparent material such as PVC or polyethylene.
The above problems have not been overcome by the winding machines of the prior art and their inability to control web tension and web severance has led to frequent web rupture and consequent machine function interruption and loss of product, to frequent core collapse due to web contraction with consequent machine function interruption and loss of product and to frequent web necking, wrinkling, creasing and other non-uniformities and core appearance distortion and again, loss of product.
Again, because of the inherent weakness of the economically acceptable hollow or tubular core structure, a difficult problem is presented to adequately support the core during winding in a manner which will enable the core to be delivered to and removed from the winding station. Also the requirement that the winding be controlled to wind an accurate length of web rather than to wind for a specific length of time has presented special problems in the feeding of the empty cores to and the removal of the wound cores from the winding assembly while at the same time ensuring positive core delivery and removal at the appropriate time.
When the core is wound with the requisite length of web the wound core is desirably required to be tabbed or labelled with a circumferentially extending, preferably central, tab adhered across the trailing edge of the web on the core, and to an under layer or portion of the web next adjacent the trailing edge, the tab having a free non adhered portion to be gripped by the fingers and pulled to commence roll unwinding. As will be appreciated, therefore, the trailing edge of the web in the wound core must be indexed accurately to enable the tabbing or labelling to be carried out automatically. Such indexing or maintenance of a constant orientation of the sometimes almost invisible trailing edge must be accomplished following high speed core rotation during winding and subsequent stoppage and delivery out of the winding apparatus and heretofor no satisfactory automatic tabbing arrangement has been provided.